A vehicle such as an automobile is generally provided with an airbag apparatus that deploys in a passenger compartment to restrain occupants in the event of an emergency such as a crash. Various types of airbag apparatuses have been developed and adopted as such an airbag, including a driver's airbag apparatus mounted inside a steering wheel, a passenger airbag apparatus mounted in an instrument panel, a side airbag apparatus mounted in a vehicle side door or an outboard side of a seat, and a knee airbag apparatus mounted under a dashboard. These airbag apparatuses are mounted inside a vehicle structure so as to be normally hidden, and are designed to split open part of the vehicle structure and inflate and deploy an airbag in a passenger compartment in the event of an emergency such as a crash. Accordingly, a fracture-opening section for an airbag must be normally covered so as to be merged with a vehicle interior surface panel, while it must split open so that an airbag smoothly and rapidly inflates and deploys in the event of an emergency.
The afore mentioned airbag apparatus includes an airbag that is normally stored in a folded state and inflates and deploys in case of an emergency, an inflator for supplying gas to the airbag, a retainer for housing the airbag, and an airbag cover that locks the retainer thereto and constitutes a vehicle interior surface panel. The airbag cover is a resin-molded, thin plate-like body and has a groove called a tear line formed on its back face. A door to be defined when the airbag cover splits open is rotatably supported by a hinge portion formed in the airbag cover and constitutes a fracture-opening section for inflating and deploying an airbag.
Various types of passenger airbag apparatuses to be mounted on an instrument panel have been developed as disclosed in Japanese Unexamined Patent Application Publication No. 2-171364 and Japanese Unexamined Patent Application Publication No. 2003-137057. The airbag apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2-171364 has an airbag cover that is formed so as to be slightly larger than an opening. During the early years of introduction of airbags, an airbag cover was often disposed only at a place necessary for the inflation and deployment of an airbag and was set into an instrument panel, as described in Japanese Unexamined Patent Application Publication No. 2-171364. However, such an airbag cover posed a problem in that it was not aesthetically pleasing because of its exposure to the front of an occupant and also it limited the flexibility of design.
As described in Japanese Unexamined Patent Application Publication No. 2003-137057, disposing an inner case having an airbag module on the back face of an instrument panel has recently become mainstream. In the case of an airbag apparatus of such a type, the instrument panel must be formed of a hard resin because of the necessity of rigidity so that it does not break away at the time of the inflation and deployment of an airbag. To attain this purpose, an inner case made of a soft resin is connected by welding to the back face of the instrument panel so that a door constituting an airbag fracture-opening section turns instead of breaking away.
However, in the case of an airbag apparatus described in Japanese Unexamined Patent Application Publication No. 2003-137057, an instrument panel and an inner case are separately constructed, which causes an increase in the number of parts and processes required for connecting them, resulting in an increase in the cost of an airbag apparatus.